I just found this page which I'm reading for breakfast. It should bring me up to date on the 360 hardware.
Edit: I found out that it was a bit outdated after I wrote this, but it was interesting reading none the less.
I'm currently trying to come up with the core engine design for the current game I'm working on with a friend of mine. Multithreading is the way to go if you've got processing needs - and even though our first game is a sprite based arcade game, it doesn't hurt to plan ahead. If all goes well we're planning on using the same core engine for other games, so it has to be able to scale up.
Check this out:
Coding For Multiple Cores on Xbox 360 and Microsoft Windows